In the prior art, measurements are made by using transducers which generate a voltage corresponding to temperature or force applied to them. This analog voltage is often converted to a digital signal for readout purposes.
The problem, however, is speed and accuracy. The parameter being measured may be in a steady state, or it may be changing rapidly. For example, in many systems, a transducer provides an analog voltage proportional to the parameter being measured. The digital output is based on an integration of the analog signal over a certain period of time, and in particular, the digital output reflects the average value of the analog output voltage over the integration period. As a result, under steady-state or near steady-state conditions, the accuracy of the digital readout will be greater with a longer integration period. Thus, where the measured parameter (e.g., weight) is not changing or is changing very slowly, the longer integration period provides a more precise digital readout.
The situation is different where the measured parameter is changing and perhaps changing rapidly. In those cases, high speed in obtaining the readout may be essential so that the ongoing process can be tightly controlled. Accuracy is important in this measurement, but speed is more critical, and as a result, a much shorter integration period is used so the results are available faster. Consequently, high speed and high accuracy are somewhat mutually exclusive in these analog-to-digital measurement systems.
The particular problem that exists in the art is when the system to be measured has phases where the parameter to be measured has both steady state or near steady state conditions as well as rapidly changing ones. An example would be an industrial vat that is being filled with several liquids, with the filling process shutting off based on the weight of the liquids in the vat. This is often done in making paint where the vat is partially filled with one liquid and then completely filled with others. The process is controlled by the weight of the vat, and it must be strictly controlled or else the color of the paint will not be consistent from vat to vat. While the vat is initially being filled with one liquid, rapid weight readouts are needed to monitor that operation closely so as to fill the vat as quickly as possible but also to reduce the flow at precisely the proper time so that neither too much nor too little of the liquid will be added. In such cases, the prior art makes a compromise with the analog-to-digital converter responsible for the measurement. The prior art simply selects one integration time which is below the optimum integration time for high resolution (long integration time) and above that for high speed (short integration time) conditions. Consequently, the device is not particularly good for either condition.
As a result, an object of this invention is to provide an analog-to-digital converter for a measurement system which provides, based on the changes or steady state nature of the measured value, high resolution in a steady state or near steady state condition and rapid readouts in changing conditions.